Companies looking to become early adopters of Microsoft's Windows x64 Edition OSes encountered a reason to postpone the decision: They may find their favorite anti-virus software no longer works on their new desktops. Microsoft maintains that most software written for older, 32-bit versions of Windows is compatible with the 64-bit version of the operating system, released in April. Due to changes to the kernel component of Windows, however, certain types of software must be rewritten for the company's 64-bit versions of Windows.

"Every time that we do a major shift in the kernel, ...any software that runs in kernel mode needs to be rewritten," said Brian Marr, senior product manager in the Windows client group at Microsoft. For the x64 Edition of Windows, that means device drivers and anti-virus software, in particular, will need to be rewritten. "Beyond that, there aren't too many types of applications that hook into the Windows kernel that deeply," Marr said.